Physical papers have been used as the primary media for information exchange for a long time and are consumed by not only inkjet printing but also laser printing. Meanwhile, graphics and texts may not be changed once printed on physical papers, making it impossible to reuse papers. As a result, the use of conventional physical papers severely wastes resources and is inconvenient in paper storing, paper carrying and paper management. With the development of display technology, E-paper has been recently proposed. The E-paper is advantageous over conventional physical papers in that it has light weight and softness so as to be carried and managed easily, it is erasable and rewritable to save resources, it displays clearly to enable a pleasing reading and so on.
Currently, E-paper is not actually used as reusable electronic paper on the contrary, it is mostly applied as display devices and made as self-driven E-book readers with display system for displaying texts and graphics. To implement a reusing E-paper, firstly, it is required a bistable E-paper, such as E-papers with electrophoretic display, cholesteryl phase display or ferroelectric LCD. And secondly, a printing device that may perform erasing and rewriting operation on E-paper over and again is needed. Thereby it can display different text and graphic information.
A laser printer among conventional physical paper printing devices will be described as an example. The printing device comprises an electrically pre-charged photosensitive selenium drum and powdered ink particles with opposite polarity as that of the drum. When printing on the physical paper by the printing device, a data signal received from a computer is transformed and then transferred to the surface of the drum, causing charges on the drum surface to change; as a result, charges on some regions of the drum surface are retained while those on other regions disappear. The regions of the drum surface which retain the charges adsorb the powdered ink particles. When the physical paper to be printed is fed into the printing device, it carries charges with the same polarity as that of the charges on the drum surface after being pressed by electrodes, though with a much larger amount, and attracts the powered ink particles on the drum surface thereto when passing through the drum, thereby forming graphics and texts on the surface of the physical paper.
A principle of displaying graphics and texts by E-papers such as the E-paper based on electrophoretic display technology is to arrange different patterns for some charged black particles and some oppositively-charged white particles. With reference to the above method for printing physical paper, when graphics and texts displayed on the E-paper are rewritten or graphics and texts are plotted on another E-paper, a voltage is applied across the E-paper to form an electric field such that the charged particles in the E-paper are moved, thereby erasing original graphics and texts on the E-paper or writing new ones onto the E-paper. Such a method is considered as a convenient and simple method. However, there is no E-paper printing device particularly designed for E-papers available now.